1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus of the scanning exposure type to be used for transferring a mask pattern onto a substrate in the lithography step for producing devices including, for example, semiconductor elements, liquid crystal display elements, plasma display elements, micromachines, and thin film magnetic heads. In particular, the present invention is preferably used when a pulse light beam is used as an exposure light beam.
2. Description of the Related Art
In order to respond to the improvement in degree of integration and degree of fineness of the semiconductor device, it is demanded to enhance the resolving power and the transfer faithfulness for the exposure apparatus to be used for the exposure step in the lithography step (representatively comprising the resist application step, the exposure step, and the resist development step) in order to produce the semiconductor device. For this purpose, the numerical aperture of the projection optical system has been hitherto gradually increased. Further, the wavelength of the exposure light beam as the exposure beam has been shortened to use the KrF excimer laser (wavelength: 248 nm) and the ArF excimer laser (wavelength: 193 nm). In the present circumstances, only the pulse light source such as the excimer laser is available as the light source of the exposure light beam having the short wavelength as described above. Further, in order to enhance, for example, the resolving power, it is also necessary to enhance the exposure amount control accuracy to expose, with a proper exposure amount, the photoresist applied onto the wafer as the substrate.
Recently, in order to enhance the throughput in the exposure step by increasing the exposure field (respective shot areas on a wafer) without increasing the size of a projection optical system, a scanning exposure type exposure apparatus (hereinafter referred to as xe2x80x9cscanning type exposure apparatusxe2x80x9d) based on the step-and-scan manner or the like has been developed, in which a reticle as a mask and the wafer are synchronously scanned with respect to the projection optical system. In the case of such a scanning type exposure apparatus, the totalized exposure amount at respective points on the wafer is averaged owing to the integration effect for the scanning direction. However, as for the non-scanning direction perpendicular to the scanning direction, for example, the influence of uneven illuminance in a slit-shaped illumination area in the non-scanning direction directly appears. As a countermeasure for this inconvenience, a method has been suggested, for example, in Japanese Patent Application Laid-Open No. 7-142313 and EP 0,633,506 A1 corresponding thereto. In this method, the shape of an opening of a field diaphragm, which defines the shape of the illumination area, is mechanically changed, or the field diaphragm is mechanically switched, in accordance with an actual totalized exposure amount.
As described above, the method for mechanically switching the shape of the field diaphragm in order to control the exposure amount in the scanning type exposure apparatus is considered to be effective when the exposure light beam is a continuous light beam such as a bright line (i-ray or the like) of a mercury lamp. However, in the present circumstances, a pulse light beam, which has a short wavelength with a relatively low oscillation frequency, is also used gradually in the scanning type exposure apparatus. When such a pulse light beam is used, in order to obtain a uniform totalized exposure amount, it is necessary to define the width of the exposure area on the wafer so that the exposure is performed substantially in an amount corresponding to an integral number of pulses at respective points on the wafer. In this case, if the shape of the opening of the field diaphragm is mechanically switched, it is feared that any area appears on the wafer, in which the condition of exposure in the amount corresponding to the integral number of pulses is not satisfied. Therefore, the method for mechanically switching the shape of the opening of the field diaphragm is not practical so much. For example, U.S. Pat. No. 6,078,381 discloses that the number of pulse light beams radiated onto respective points on the wafer is adjusted to be an integral number.
When the exposure light beam is an ultraviolet light beam, the following inconvenience sometimes arises. That is, any cloudiness gradually appears on a surface of an optical member for constructing the illumination optical system or the projection optical system, for example, due to the reaction between the exposure light beam and organic compounds in the atmosphere. As a result, the transmittance of the optical system is lowered over a long period of time. Further, the following phenomenon is also known. That is, when the exposure light beam is a pulse light beam in a vacuum ultraviolet region at a wavelength of not more than about 200 nm, the refractive member in the illumination optical system or the projection optical system is gradually deteriorated, for example, due to the so-called compaction. As a result, the transmittance is gradually varied. The variation of the transmittance also depends on the optical path for the exposure light beam. Therefore, for example, if the state, in which the distribution of the exposure light beam on the pupil plane is non-axisymmetric (asymmetric with respect to an axis), is continued, for example, when the so-called modified illumination method is used, the variation of the transmittance of the refractive member is also non-axisymmetric. As a result, it is feared that the distribution of illuminance is not uniform in the non-scanning direction in the illumination area (or the exposure area), and the unevenness of the totalized exposure amount is increased. Further, if the variation of the transmittance occurs about the center of any point other than those disposed on the optical axis, it is also feared that the collapse amount of the telecentricity (telecentric property) of the exposure light beam with respect to the reticle or the wafer exceeds an allowable range.
As described above, for example, if any time-dependent variation of the transmittance distribution occurs due to the cloudiness or the deterioration of the optical member, and the illuminance distribution in the illumination area (or the exposure area) is nonuniform in the non-scanning direction, then the nonuniformity can be improved by exchanging the concerning optical member. However, it takes a fairly long period of time to perform the exchange. Further, it is also conceived that any mechanism for exchanging the optical member is provided. However, in such a case, the exposure apparatus has a large size, and the production cost is increased as well.
Taking the foregoing viewpoints into consideration, a first object of the present invention is to provide an exposure method which makes it possible to enhance the uniformity of a totalized exposure amount on a wafer or the telecentricity of a exposure light beam when the exposure is performed in accordance with the scanning exposure system.
A second object of the present invention is to provide an exposure method which makes it possible to enhance the uniformity of a totalized exposure amount on a wafer when the scanning exposure is performed by using a pulse light beam as an exposure light beam.
A third object of the present invention is to provide an exposure method which makes it possible to easily enhance the uniformity of a totalized exposure amount on a wafer or the telecentricity of a exposure light beam even in the case of the occurrence of any variation in optical characteristic of an optical member or an optical system on an optical path of the exposure light beam up to the wafer, for example, any variation in transmittance (including variation in reflectance) when the exposure is performed in accordance with the scanning exposure system.
Still another object of the present invention is to provide an exposure apparatus which makes it possible to use the exposure method as described above, and a method for producing highly accurate devices based on the use of the exposure method.
A first exposure method according to the present invention lies in an exposure method for exposing a substrate with an exposure light beam by illuminating a mask (R) with the exposure light beam and synchronously scanning the mask and the substrate (W); the exposure method comprising controlling a transmittance with respect to the exposure light beam with a predetermined distribution in a non-scanning direction (X direction) intersecting a scanning direction (Y direction) for the substrate.
According to the present invention as defined above, for example, when the transmittance of a transmissive member or the reflectance of a reflective member of an exposure light beam-radiating system (for example, an illumination system or a projection system), and the entire transmittance ranging, for example, from a position for monitoring the energy of the exposure light beam to the substrate is gradually varied, then the transmittance for the exposure light beam is controlled with such a distribution as to offset the variation amount in the non-scanning direction thereof. Accordingly, the uneven illuminance in the non-scanning direction on the substrate is decreased. Consequently, the uniformity of the totalized exposure amount after the scanning exposure on the substrate is improved. Further, for example, when the transmittance for the exposure light beam is varied about the center of the point deviated from the optical axis, the telecentricity of the exposure light beam is changed on the mask or the substrate. Therefore, the transmittance for the exposure light beam is controlled so that the transmittance variation is offset. Accordingly, even when the height of the mask or the substrate is changed, for example, no positional deviation occurs in the projected image.
In the present invention, when the exposure light beam is a pulse light beam, it is desirable that a width in the scanning direction for the substrate in an exposure area (35P) of the exposure light beam on the substrate is determined so that the exposure light beam is radiated substantially as an integral number of pulses with respect to any point as an exposure objective during a period in which the point as the exposure objective on the substrate passes over the exposure area. When the scanning exposure is performed while increasing the scanning velocity of the substrate in order to increase the throughput under a condition in which the frequency of the pulse light beam is not so high, for example, when an excimer laser light beam is used as the exposure light beam, it is feared that the unevenness of the totalized exposure amount of a degree corresponding to about one pulse at the maximum occurs on the substrate, unless the exposure is performed in an amount corresponding to an identical integral number of pulses for the respective points on the substrate. In relation to such a situation, the width of the exposure area in the scanning direction is fixed in the present invention, and the transmittance itself for the exposure light beam is controlled. Therefore, it is possible to simultaneously satisfy both the condition to perform the exposure with the integral number of pulses and the control of the uneven illuminance in the non-scanning direction.
It is desirable that the transmittance for the exposure light beam is controlled after uniformity of an illuminance distribution of the exposure light beam is enhanced by the aid of one stage of optical integrator (uniformizer or homogenizer) or a plurality of stages of optical integrators (6, 9). For example, the time-dependent variation of the transmittance distribution of the radiating system can be corrected easily and highly accurately by controlling the transmittance after the passage through the optical integrator as described above.
It is desirable that uneven illuminance in the non-scanning direction of the exposure light beam with respect to the substrate is corrected by controlling the transmittance for the exposure light beam by varying the distribution of the transmittance for the exposure light beam in the non-scanning direction. Even when any uneven illuminance of the exposure light beam occurs in the scanning direction on the substrate, any unevenness of the totalized exposure amount is not substantially caused owing to the integration effect brought about by the scanning exposure. On the contrary, the integration effect is not exerted in the non-scanning direction of the substrate. Therefore, the uniformity of the totalized exposure amount in the non-scanning direction is improved by previously avoiding any occurrence of the uneven illuminance in the non-scanning direction.
Further, the transmittance for the exposure light beam may be previously allowed to have a predetermined variable distribution in the scanning direction for the substrate as well. The collapse amount of the telecentricity of the exposure light beam with respect to the mask or the substrate may be corrected by controlling the transmittance for the exposure light beam. The totalized exposure amount is scarcely affected even when the transmittance distribution is provided in the scanning direction. However, it is possible to correct the collapse amount of the telecentricity in the scanning direction.
In order to control the transmittance for the exposure light beam as described above, for example, it is desirable that the exposure light beam is partially shielded with a transmittance distribution control member (23A, 23B) which has a variable transmittance distribution in the non-scanning direction for the substrate, in an area defocused by a predetermined spacing distance with respect to a plane of a pattern formed on the mask (a pattern plane of the mask) or a conjugate plane conjugate with the pattern plane. The image of the shielding pattern of the transmittance distribution control member is fuzzy (becomes blur) on the mask by partially shielding the exposure light beam in the area defocused from the pattern plane of the mask (or the conjugate plane therewith) as described above. Therefore, the exposure light beam is successively radiated substantially uniformly onto all of the points on the substrate. Thus, the uniformity of the totalized exposure amount distribution is improved.
For example, it is desirable that the transmittance distribution control member is provided with a first set of a plurality of shielding lines (28A, 29A) in each of which a shielding area is changed in a predetermined distribution in the non-scanning direction for the substrate, and a second set of a plurality of shielding lines (28B, 29B) each of which has substantially the same shape as that of the shielding line of the first set; and any one of the following operations is selectively used, i.e., the operation in which the first set of the shielding lines and the second set of the shielding lines are inserted/withdrawn substantially symmetrically in the scanning direction for the substrate with respect to the optical path of the exposure light beam, and the operation in which the plurality of shielding lines of the first set and the second set are moved in the non-scanning direction for the substrate respectively. For example, the shielding line may be an aggregate of minute dot patterns, or it may be a semitransparent pattern for transmitting the exposure light beam to some extent.
The axisymmetric convex uneven illuminance or the concave uneven illuminance can be corrected without affecting the telecentricity by inserting/withdrawing the two sets of the shielding lines substantially symmetrically in the scanning direction. On the other hand, the convex or concave uneven illuminance deviated from the optical axis or the uneven illuminance inclined in the non-scanning direction can be corrected by moving the two sets of the shielding lines in the non-scanning direction respectively.
It is desirable that the first set of the plurality of shielding lines (28A, 29A) are arranged at a pitch which is gradually changed in the scanning direction for the substrate. Accordingly, the occurrence of any diffraction pattern (i.e., uneven illuminance) of the exposure light beam is avoided, which would be otherwise caused by the plurality of shielding lines. The same or equivalent effect is also obtained by slightly inclining the plurality of shielding lines arranged at a substantially constant pitch with each other.
When the exposure light beam is a pulse light beam, it is desirable that the first set of the plurality of shielding lines are arranged at different pitches therebetween which are different respectively from a length obtained by converting a spacing distance of movement of the substrate during each cycle of pulse light emission of the exposure light beam into a spacing distance at a position of each of the first set of the plurality of shielding lines. Accordingly, it is possible to avoid any transfer of a defocused image of a certain shielding line onto the substrate.
It is desirable that the transmittance distribution control member further comprises a third set of a plurality of shielding lines (26A to 26C, 27A to 27C) which have a large amount of change of a shielding area in the non-scanning direction for the substrate as compared with the first set and the second set of the plurality of shielding lines; and the third set of the plurality of shielding lines are moved in at least one of the scanning direction and the non-scanning direction for the substrate with respect to the optical path of the exposure light beam, in order to roughly correct any uneven illuminance of the exposure light beam in the non-scanning direction.
A second exposure method according to the present invention lies in an exposure method for exposing a substrate with an exposure light beam by illuminating a mask with the exposure light beam and scanning the substrate across the exposure light beam via the mask, the exposure method comprising:
measuring uneven illuminance on a substrate plane or at a position in the vicinity thereof;
controlling an illuminance distribution of the exposure light beam in a non-scanning direction intersecting a scanning direction for the substrate on an optical path of the exposure light beam on the way to the substrate to correct the measured uneven illuminance; and
synchronously moving the mask and the substrate with respect to the exposure light beam to scan the substrate across the exposure light beam in which the uneven illuminance is corrected. According to this exposure method, the measured uneven illuminance in the non-scanning direction is effectively corrected by controlling the illuminance distribution of the exposure light beam.
In still another aspect, a first exposure apparatus according to the present invention lies in an exposure apparatus for exposing a substrate with an exposure light beam via a pattern on a mask by illuminating the mask (R) with the exposure light beam from an exposure light source (1) and synchronously scanning the mask and the substrate (W); the exposure apparatus comprising a transmittance distribution control member (23A, 23B, 24) which is arranged in an area defocused by a predetermined spacing distance with respect to a pattern plane of the mask or a conjugate plane conjugate with the pattern plane and which partially shields the exposure light beam with a variable transmittance distribution in a non-scanning direction intersecting a scanning direction for the substrate; and a driving unit (20) which drives the transmittance distribution control member in order to control the transmittance distribution in the non-scanning direction for the exposure light beam. The exposure method of the present invention can be carried out by using the exposure apparatus as defined above.
It is desirable that the exposure light source is a pulse light source; the apparatus further comprises a fixed field diaphragm (17) which is arranged on a plane defocused by a spacing distance smaller than a defocus amount of the transmittance distribution control member with respect to the pattern plane of the mask or the conjugate plane conjugate with the pattern plane; and a width of the field diaphragm in a direction corresponding to the scanning direction for the substrate is determined so that the exposure light beam is radiated substantially as an integral number of pulses to any point as an exposure objective during a period in which the point as the exposure objective on the substrate passes over an image of the field diaphragm.
It is desirable that one stage or a plurality of stages of optical integrators (6, 9) are arranged between the exposure light source and the transmittance distribution control member.
It is desirable that the transmittance distribution control member is provided with a first set of a plurality of shielding lines (28A, 29A) in each of which a shielding area is gradually changed in the non-scanning direction for the substrate, and a second set of a plurality of shielding lines (28B, 29B) each of which has substantially the same shape as that of the shielding line of the first set. It is desirable that the transmittance distribution control member further comprises a third set of a plurality of shielding lines (26A to 26C, 27A to 27C) which have a large amount of change of a shielding area in the non-scanning direction for the substrate as compared with the first set and the second set of the plurality of shielding lines.
A second exposure apparatus according to the present invention lies in an exposure apparatus for exposing a substrate with an exposure light beam via a pattern on a mask by illuminating the mask with the exposure light beam and synchronously scanning the mask and the substrate; the exposure apparatus comprising a measuring unit which measures uneven illuminance of the exposure light beam in a non-scanning direction intersecting a scanning direction for the substrate; a shield plate which has a shielding pattern for adjusting an illuminance distribution of the exposure light beam in the non-scanning direction; a driving unit which drives the shield plate; and a control unit which displaces the shield plate in a path for the exposure light beam by controlling the driving unit so that the uneven illuminance is corrected. According to this exposure apparatus, the measured uneven illuminance in the non-scanning direction is effectively corrected by means of the shield plate for adjusting the illuminance distribution of the exposure light beam.
The second exposure apparatus may further comprise an exposure light source, wherein the exposure light source generates a pulse beam having an oscillation frequency which is less than 10 KHz. The plate may be formed with shielding patterns which extend in the non-scanning direction and which have different shielding areas in the non-scanning direction. The exposure apparatus may further comprise a memory which stores a previously determined relationship between the uneven illuminance and an uneven illuminance correction amount depending on a driving amount of the plate; and a telecentricity-measuring unit. It is desirable that the plate is arranged at a position at which an image of the pattern formed on the plate is defocused on a conjugate plane with respect to a pattern plane of the mask, and a defocus amount xcex4Z satisfies xcex4Z greater than FD/(2xc2x7NA) with respect to a numerical aperture NA of the exposure light beam on the plate and a maximum line width FD of the shielding pattern in the scanning direction.
The exposure apparatus may further comprise a timer and a memory which stores a previously determined relationship between working time of the exposure apparatus and the uneven illuminance, wherein the control unit may correct the uneven illuminance by automatically controlling the driving unit depending on exposure time measured by the timer. The driving unit of the exposure apparatus may include a slider which is moved while holding each of the first, second, and third correcting plates, a guide with which the slider is engaged, and a motor which moves the slider.
In still another aspect, a third exposure method according to the present invention lies in an exposure method for exposing a substrate with an exposure light beam via a pattern on a mask by illuminating the mask (R) with the exposure light beam subjected to pulse light emission and synchronously scanning the mask and the substrate (W), wherein an illuminance distribution of the exposure light beam on the substrate is set to be trapezoidal with respect to a scanning direction of the substrate, and a width (DE) of an inclined portion (67Ba, 67Bb) of the trapezoidal illuminance distribution is set to be substantially an integral multiple of a distance of movement of the substrate in the scanning direction during a period of one cycle of the pulse light emission of the exposure light beam. As a result, the exposure light beam effects the exposure for respective points in a common amount of an integral number of pulses during the period in which the respective points on the substrate are moved over the inclined portion of the illuminance distribution during the scanning exposure. Therefore, the totalized exposure amount is made to be uniform.
In this arrangement, it is desirable that a shape of an exposure area brought about by the exposure light beam on the substrate is set so that a width (D(X)) is gradually changed with respect to a non-scanning direction intersecting the scanning direction for the substrate depending on a totalized exposure amount distribution on the substrate. The uniformity of the totalized exposure amount is improved by changing the width of the exposure area in the scanning direction so that the distribution of the totalized exposure amount in the non-scanning direction is constant.
A third exposure apparatus according to the present invention lies in an exposure apparatus for illuminating a mask with an exposure light beam and exposing a substrate with the exposure light beam via the mask, the exposure apparatus comprising:
an illuminance-correcting member which is arranged in an area defocused with respect to a conjugate plane conjugate with the substrate and which partially shields the exposure light beam with a variable transmittance distribution; and
a control unit which sets the transmittance distribution of the exposure light beam so as to correct at least one of uneven illuminance and a collapse amount of telecentricity of the exposure light beam with respect to the mask or the substrate.
A fourth exposure method according to the present invention lies in an exposure method for exposing a substrate with an exposure light beam via a mask by relatively moving the mask and the substrate with respect to the exposure light beam subjected to pulse oscillation, wherein:
an illuminance distribution of the exposure light beam concerning a scanning direction for the substrate is set to be substantially trapezoidal, a width of the exposure light beam in the scanning direction is allowed to partially differ, and a scanning exposure condition for the substrate is set so that an integral number of pulses of the exposure light beam are radiated onto a point as an exposure objective during a period in which the point as the exposure objective on the substrate passes over an inclined portion of the illuminance distribution.
A method for producing a device according to the present invention comprises the step of transferring a device pattern (R) onto a workpiece (W) by using the exposure method of the present invention. The uniformity of the totalized exposure amount is improved by the present invention. Therefore, it is possible to highly accurately mass-produce devices having high degrees of integration.